THE mass shooting at a Walmart store in El Paso, Texas, earlier this month was widely reported as a racially motivated attack by a white supremacist. That is almost certainly what it was: shortly before it happened, a manifesto railing against the “Hispanic invasion” of the US appeared online, and the police believe it was posted by the shooter.

As has become depressingly familiar, the document contained numerous references to alt-right conspiracy theories such as the “great replacement”, which claims that white Christian civilisation is being swamped by black and Asian people, and Muslims. But buried in …